The present invention generally relates to a comprehensive or all-round control system for a power train system of an automobile or motor vehicle. More particularly, the invention is concerned with a torque control method and an apparatus for carrying out the same which can profitably ensure high-efficiency operation of an internal combustion engine (hereinafter also referred to as the engine for short).
In a motor vehicle equipped with an automatic transmission gear (also known as the automatic speed change gear) and an electrically controlled throttle, such an engine torque control is adopted that a driving power (driving torque) required by the motor vehicle is determined on the basis of detection signals outputted, respectively, from an accelerator pedal stroke sensor (i.e., a sensor for detecting a stroke or depression depth of the accelerator pedal of the motor vehicle) and a vehicle speed sensor (i.e., sensor for detecting a speed of the motor vehicle), as is disclosed in, for example, JP-A-3-163256 (Japanese Unexamined Patent Application Publication No. 163256/1991). Parenthetically, this literature will hereinafter be referred to as the first related art. In that case, the driving power (driving torque) is determined by resorting to a fuzzy estimation procedure which is based on a fuel cost preference rule, a torque transmission performance preference rule and an engine noise suppression preference rule, wherein the gear position (speed change position) of the automatic transmission and the throttle opening degree which correspond to the desired driving power (driving torque) are arithmetically determined or calculated. On the basis of the values as determined, the automatic transmission and the throttle opening degree are controlled. The three rules mentioned above constitute a fuzzy set with a speed ratio (i.e., the ratio between the output shaft rotation number of the torque converter and the input shaft rotation number thereof) being used as a parameter, wherein the membership function of the fuzzy set is determined with reference to the desired speed ratio determined according to the three rules mentioned above. For more particulars, reference should be made to the first related art mentioned above.
On the other hand, the fuel-cost improvement of the motor vehicle presents a problem which is incessantly tackled with for solution. To this end, there has been proposed in conjunction with the internal combustion engine equipped with the electronically controlled throttle a method of arithmetically determining the opening degree of the throttle valve and the gear ratio of the transmission gear which are required for realizing a minimum fuel cost (l/Km) (i.e., a minimum fuel consumption per unit running or travel distance of the motor vehicle) on the basis of the stroke (depression depth) of the acceleration pedal and the vehicle speed of the motor vehicle, wherein the throttle valve and the gear ratio of the transmission gear are determined so that the minimum fuel cost can be achieved. Typical examples of this method are disclosed in JP-A-62-26134 (also referred to as the second related art) and JP-A-3-163256.
Incidentally, the fuel cost may also be defined as a running distance (Km/l) per unit fuel consumption. However, in the following description, it is assumed that the fuel cost is given by a fuel consumption per unit distance (i.e., l/Km).
Further, there is known an approach for decreasing the fuel cost by reducing the less (pumping loss) due to engine suction resistance (negative pressure resistance) by using the engine torque in the vicinity of the maximum value thereof at each of the gear ratios, as is disclosed in Otto Holzinger et al.: "Automotive Electronics-Integration and Partitioning", Robert Bosch GmbH, Vehicle Electronics Meeting Society's Needs: Energy, Environment, Safety, Proceedings of the 1992 International Congress on Transportation Electronics, P-260, pp. 247-252 (named the third related art).